The Japanese American soldiers became the most decorated unit in U.S. history. Inouye fought in Italy and France, losing his right arm during a 1945 battle against the Germans. He would ultimately be awarded the Medal of Honor, the highest citation for combat heroics.

Inouye returned hometo become a towering figure in Hawaii politics, joining the first delegation that the new state sent to Congress in 1959, then winning election to the Senate in 1962.

When he died Monday of respiratory complications at Walter Reed National Military Medical Center in Bethesda, Md., Inouye was the second-longest-serving senator in U.S. history. He was 88.

In the Senate, the Democrat was a low-key presence, and, as an amputee, a walking testament to the understated valor of his generation.

"Tonight, our country has lost a true American hero," President Obama said in a statement. "In Washington, he worked to strengthen our military, forge bipartisan consensus, and hold those of us in government accountable to the people we were elected to serve."

But, the president added, "it was his incredible bravery during World War II … that made Danny not just a colleague and a mentor, but someone revered by all of us lucky enough to know him."

The country's first Japanese American senator, Inouye was reelected eight times, most recently in 2010. He served nearly 50 years in the Senate, second only to West Virginia Sen. Robert C. Byrd, who was in his 51st year in the chamber when he died in 2010.

Inouye earned a reputation as a politician who could deliver money and projects to his home state, often through so-called earmarks. From 1998 to 2003, he steered $1.4 billion to military projects in Hawaii while serving as chairman of the defense appropriations subcommittee, according to the National Journal Almanac.

In 2009 he became chairman of the powerful Senate Appropriations Committee and continued directing money back home, boasting about his ability to secure spending for pet projects even after the controversial practice fell out of fashion.

"I'm the No. 1 earmarks guy in the U.S. Congress," he told a group of Hawaii business leaders that year, according to the Honolulu Star-Bulletin.

He supported the military, but was skeptical of war. He voted against the Iraq war resolution in 2002, and was among the 12 Democrats who voted in 2006 to withdraw all combat troops from Iraq by July 2007.

On the national stage, he was also known for his service on the Senate Watergate Committee and later chaired the Senate committee that investigated the Iran-Contra scandal during the Reagan administration.

During the Watergate hearings, millions of network television viewers saw Inouye grill top White House aides, including H.R. Haldeman and John D. Ehrlichman.

At one point Inouye, believing a microphone was turned off, whispered, "What a liar!" about Ehrlichman.

The next week, Ehrlichman's attorney, John J. Wilson, referred to Inouye as "that little Jap." Inouye received thousands of telegrams and letters of support.

In the summer of 1987, Inouye rebuked Marine Lt. Col. Oliver North, a key figure in the Iran-Contra scandal, which involved the sale of embargoed weapons to Iran in order to divert the resulting profits to anti-communist rebels in Nicaragua.

"It was painful to all of us to sit here and listen to your testimony," the senator said. "It was equally painful that you lied and misled for what you believed to be a good cause."

"Everyone in the Senate not only admired Danny Inouye, but they trusted him," Vice President Joe Biden said in a statement. "We all knew he would do the moral thing regardless of the consequences — whether it was passing judgment on a president during Watergate or on another president in the Iran-Contra hearings. And Danny always remembered where he came from — and how hard his family had to struggle."

Daniel Ken Inouye was born in Honolulu on Sept. 7, 1924, the oldest of four children of Japanese immigrants. His father was a jewelry clerk and his mother a homemaker.

Following the 1941 attack on Pearl Harbor, about 110,000 Pacific Coast residents — but not those in Hawaii — were interned in detention camps. Inouye, who continued in a pre-med program at the University of Hawaii, waited impatiently until he could enlist.